The present invention relates to novel nano-array electrodes with a controlled nano-structure and photoelectric conversion devices using the same.
Conventional electrooptic devices and photoelectrochemical devices usually contain functional electrodes wherein a semiconductor is formed as a film on a substrate with an electrically conductive film. The semiconductor is responsive to external factors such as heat, light and temperature changes and produces electrons, phonons, or complexes thereof depending on the environment. When these electrons, phonons, or complexes thereof propagate through a semiconductor layer which is formed of aggregated semiconductor fine particles, scattering of the fine particles therein causes the deactivation of their elementary excitation state, which will be a problem when the performance of a functional device is intended to be improved. Therefore, it is important to suppress the scattering of the fine particles in the agglomerate thereof.
For example, the most commonly used semiconductor material for dye-sensitized solar cells is titanium oxide (see, for example, Document 1 given below). The solar cells includes functional electrodes formed by forming a film of titanium oxide particles a few tens of nanometers in size on a transparent electrically conductive substrate and allowing a dye to adsorb thereon. It has been reported that the photo-conversion efficiency of this functional electrode depends largely on the structure of the titanium oxide layer such as the shape of titanium oxide particles and the bonding state thereof. The portions wherein titanium oxide particles bond to each other form barriers to the passage of photo-generated electrons through the titanium oxide layer to the transparent electrically conductive substrate. Due to the formation of the barriers, sufficient advantageous effects to enhance the solar energy conversion efficiency have not been able to be obtained even though the titanium oxide layer is thickened and a larger amount of dye is adsorbed thereto. In order to enhance the solar energy conversion efficiency, it has been attempted to control the structure of titanium oxide particles forming the titanium oxide layer (see, for example, Documents 2 to 8). However, it is difficult to accurately control the structure of particles, and at the same time an issue concerning the enhancement of the productivity also arises.
For enhancing the efficiency of an organic film type solar cell, it is necessary to establish a combination of an electron-donating organic semiconductor (donor) and an electron-accepting organic semiconductor (acceptor), a so-called heterojunction structure. An effective charge separation occurs in the proximity of the interface between the donor and the acceptor. Based on such an idea, Patent Documents 1 and 2 below proposed the use of a so-called bulk heterojunction wherein an electric conductive polymer as a donor and a fullerene derivative as an acceptor are mixed, thereby successfully developing a device with higher photoelectric converting efficiency than the conventional layered structure devices. In order to further enhance the efficiency, it is necessary to precisely control the interface structure between the donor and acceptor. However, there is a problem that it is difficult to control the structure by the mere mixing of the donor and acceptor.    Patent Document 1: U.S. Pat. No. 5,454,880    Patent Document 2: U.S. Pat. No. 5,331,183    Non-Patent Document 1: “NATURE” (Great Britain) 1991, VOL. 353, page 737 by B. O'Regan and M. Gratzel    Non-Patent Document 2: “Nano Letters” (U.S.A.) 2001, VOL. 1, page 637 by M. S. Won, Esther S. Jeng, and Jackie Y. Ying    Non-Patent Document 3: “Journal of American Chemical Society” (U.S.A.) 1998, VOL. 120, page 6832 by M. Ohtaki et al.    Non-Patent Document 4: “Advanced Materials” (U.S.A.) 2002, VOL. 14, page 309 by M. Yata, M. Mihara, S. Mouri, M. Kuroki, and T. Kijima    Non-Patent Document 5: “Chemical Communications” (Great Britain) 1996, page 1685 by N. Ulagappan and C. N. R. Rao    Non-Patent Document 6: “Chinese Journal of Catalysis” (China) 1999, VOL. 20, page 375 by W. Zhao, Y. Sun, Q. Ma, and Y. Fang    Non-Patent Document 7: “Microporus and Mesoporous Materials” (U.S.A.) 1999, VOL. 30, page 315 by D. M. Antonelli    Non-Patent Document 8: “Journal of Materials Chemistry” (Great Britain) 1999, VOL. 9, page 2971 by H. Imai, Yuko Takei, Kazuhiko Shimizu, Manabu Matsuda, and Hiroshi Hirashima